Jetpack Compose Navigation - pass argument to startDestination

Question

The app I'm building uses compose navigation with routes. The challenge is that the start destination is dynamic.

Here is a minimal example:

class MainActivity : ComponentActivity()
{
    override fun onCreate(savedInstanceState: Bundle?)
    {
        super.onCreate(savedInstanceState)

        setContent {
            val navController = rememberNavController()

            NavHost(
                navController = navController,
                startDestination = "dynamic/1", // doesn't work
                // startDestination = "static", // workaround
            ) {
                composable(
                    route = "dynamic/{$ARG_ID}",
                    arguments = listOf(navArgument(ARG_ID) { type = NavType.StringType }),
                ) {
                    val id = it.arguments?.getString(ARG_ID)
                    Text("dynamic route, received argument: $id!")
                }
                // part of the workaround
                // composable(
                //  route = "static",
                // ) {
                //  LaunchedEffect(this) {
                //      navController.navigate("dynamic/1")
                //  }
                // }
            }
        }
    }

    companion object
    {
        const val ARG_ID = "id"
    }
}

The app crashes with

java.lang.IllegalArgumentException: navigation destination route/1 is not a direct child of this NavGraph

The problem only exists if the "dynamic" route is used as start destination. This can be verified by using startDestination = "static".

Although, the "static" route workaround works I'm looking for a solution without it because it kind of obfuscates the code and also creates an additional entry in the back stack.

-> Full code sample to reproduce the issue

Related SO questions

• Navigation Architecture Component- Passing argument data to the startDestination - Answers don't seem to be applicable to Compose Navigation.
• Pass an argument to a nested navigation graph in Jetpack Compose - No answer given.
• Compose Navigation - navigation destination ... is not a direct child of this NavGraph - The accepted answer doesn't resolve the issue.

Edit:

I want to stress that the original sample used to not contain the "static" composable. I only added the "static" composable to have a working startDestination and to prove that the "dynamic" composable can be navigated to.

Update:

Even switching to the query parameter syntax for optional arguments, providing a default value, and setting the start destination without any argument does not work.

The following variation

NavHost(
    navController = navController,
    startDestination = "dynamic",
) {
    composable(
        route = "dynamic?$ARG_ID={$ARG_ID}",
        arguments = listOf(navArgument(ARG_ID) { type = NavType.StringType; defaultValue = "1" }),
    ) {
        val id = it.arguments?.getString(ARG_ID)
        Text("dynamic route, received argument: $id!")
    }
}

Leads to the exception

java.lang.IllegalArgumentException: navigation destination dynamic is not a direct child of this NavGraph

Answer 1

Full credit goes to ianhanniballake, who explained the solution to me in a comment. I'm going to show the working version of my code sample here.

The big insight to me was:

startDestination must not match a composable route in the sense of pattern matching but it must be exactly the same string.

That means an argument can't be set via startDestination directly but has to be set via the argument's defaultValue.

Here is the working sample:

class MainActivity : ComponentActivity()
{
    override fun onCreate(savedInstanceState: Bundle?)
    {
        super.onCreate(savedInstanceState)

        setContent {
            val navController = rememberNavController()

            NavHost(
                navController = navController,
                // 1st change: Set startDestination to the exact string of route
                startDestination = "dynamic/{$ARG_ID}", // NOT "dynamic/1", provide arguments via defaultValue
            ) {
                composable(
                    route = "dynamic/{$ARG_ID}",
                    // 2nd change: Set startDestination argument via defaultValue
                    arguments = listOf(navArgument(ARG_ID) { type = NavType.StringType; defaultValue = "1" }),
                ) {
                    val id = it.arguments?.getString(ARG_ID)
                    Text("dynamic route, received argument: $id!")
                }
            }
        }
    }

    companion object
    {
        const val ARG_ID = "id"
    }
}

The approach equally works with the argument provided in the form of a query parameter.

To be honest, I see this as a small limitation because the start route now dictates what has to be the defaultValue. I might want to set a different defaultValue or none at all. Yet, in most cases this should be the most elegant solution.

Answer 2

All credit goes to ianhanniballake and Peter. In my case I didn't add any additional (mandatory key/optional key) in route for the argument data. I kept the route clean like below:

Nav graph:

 navigation(route = Route.Root.route, startDestination = Route.SubmitForm.route) {

    composable(
        route = Route.SubmitForm.route,
        arguments = listOf(
            navArgument(ARG_KEY) {
                type = NavType.StringType
                defaultValue = JsonConverter.toJson(user, User::class.java)
            },
        )
    )
}

Route sealed class:

sealed class Route(val route: String) {
    object MyRoute : Route("$ROOT/submit-form")
}

And in view model just get the data like this:

@HiltViewModel
class MyViewModel @Inject constructor(
    stateHandle: SavedStateHandle,
) : ViewModel {

    lateinit var user

    init {
        user = stateHandle.get<String>(ARG_NAME) // Supported data types
    }
}

It worked for me.